Apicomplexan parasites, Toxoplasmaand Plasmodiumare two of the most prevalent and important parasitic diseases of mankind. The success of this class of parasite lies in their ability to form parasite vacuoles (PVs) that avert fusion with and destruction by host cell lysosomes. We have recently discovered a novel pathway for immune destruction of these parasites by disruption of the PV membrane and subsequent formation of an autophagic vacuole around the exposed pathogen. Using a newly developed ex vivo assay for intracellular killing of Toxoplasma gondii parasites by primed macrophages, we will first define the individual and combined roles of IFN-gamma receptor signaling and IGTP versus CD40 and TNF-receptor signaling in mediating autophagic elimination of the parasite. We will also determine whether virulent strains of the pathogen have developed and produce factor(s) that block the ability of the primed macrophages to eliminate invasive parasites. The ability of anti-CD40 treatment to surmount a blockade of this host defense response by virulent strains of the parasite or by genetic deficiencies in the IFN-gamma response pathway will be evaluated. The proposed research will advance basic understanding of the immune host-parasite relationship and pinpoint specific strategies for boosting host defenses to intracellular pathogens via induction of autophagy. PUBLIC HEALTH RELEVANCE: Infections caused by apicomplexan parasites, toxoplasmosis and malaria are two of the most important parasite diseases of mankind. We have recently described a new mechanism for immune clearance of this type of parasite by pathogen vacuole disruption and autophagic elimination. In this NIH exploratory proposal, our studies will yield important information how the immune response is regulated and can be manipulated to promote this type of anti-parasite host defense.